Polyurethanes are extremely versatile materials and have been used in a wide variety of applications such as foam insulation, car seats and abrasion resistant coatings. Polyurethanes are used in a wide variety of forms, for example non-cellular materials such as elastomers; and cellular materials such as low density flexible foams, high density flexible foams, and microcellular foams. Microcellular foams have been used for energy absorbing bumper mountings and auxiliary suspension units for wheels, and in particular in shoe soles.
Microcellular polyurethane foams used in shoe soles require a wide range of properties such as resistance and durability in actual use, combined with high flexibility, optimal impact resilience, low weight, high thermal insulation and cushioning. There is a need for microcellular polyurethane foams to provide an improvement in one or more of the aforementioned properties. In particular, known shoe soling materials tend to have insufficient flexibility on repeated flexing at low temperature (due to strain hardening), and hydrolytic instability.